Means and method of chemical production

ABSTRACT

Disclosed is a process for manufacturing bleach (or sodium hypochlorite) and caustic potash (or KOH) without the need for shipping or storing chlorine gas. Specifically, the present invention relates to the manufacture of potassium hydroxide and chlorine gas, through several process options, for the manufacture of sodium hypochlorite (or bleach), hydrochloric acid (HCl) and/or other chlorinated compounds. The disclosed process allows operating flexibility based on chlorine demand, reduces capital costs, and eliminates the need for the transportation and storage of chlorine gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.10/913,954, filed Aug. 6, 2004, which claims priority to ProvisionalApplication Ser. No. 60/493,435, filed on Aug. 8, 2003, the contents ofthe entire chain of applications is herein incorporated by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates to a means for producing bleach (sodiumhypochlorite) and potassium hydroxide (KOH) using chlorine gas producedon-site from electrolysis of potassium chloride. More specifically, theinvention relates to a process that will allow the manufactured chlorinegas to be sold directly to an adjacent plant, or to be used onsite forthe manufacture of hydrochloric acid and/or bleach. The flexibility ofthis process provides unique operating alternatives based on currentmarket demand and never requires the transportation of or the onsitestorage of the extremely hazardous chlorine gas.

BACKGROUND OF THE INVENTION

Currently, all potassium hydroxide plants in the United States sellliquid chlorine and potassium hydroxide. Chlorine and potassiumhydroxide are transported by rail to customers. At present, five plantsproduce chlorine and potassium hydroxide. Potassium chloride and waterare electrolyzed to produce chlorine, potassium hydroxide, and hydrogenaccording to the following reaction:

2KCl+2H₂O->Cl₂+2KOH+H₂

Between 2,400 and 3,200 kiloWatt hours per ton of chlorine produced areneeded for this reaction depending on the electrolysis technology.

Chlorine, potassium hydroxide and hydrogen are produced from an aqueouspotassium chloride solution by mercury, asbestos diaphragm or membranecell electrolysis. With some variations, the usual process involvesbrine purification and de-ionization, electrolysis, chlorine processing,potassium hydroxide processing, and hydrogen processing.

Processes for potassium hydroxide (KOH) production are well known inprior art. One such process is depicted in FIG. 1. Solid potassiumchloride (KCl) salt 1 arrives at a processing plant via rail car 4.Potassium chloride 1 is transferred to a salt dissolver 2, wherein thesolid, impure potassium chloride 1 is dissolved in water to form brine3. At some plants, sodium chloride (NaCl) is substituted for potassiumchloride to ultimately produce sodium hydroxide (NaOH) instead ofpotassium hydroxide (KOH). Next, appropriate chemicals are added to thebrine 3 to precipitate impurities. The resulting mixture is fed to athickener 5, from which precipitates and clarified raw brine 3 areseparately withdrawn. The clarified brine 3 is then filtered by brinefilter 6. Solid precipitates are sent to a landfill, or disposed of byany suitable method. The filtered brine 3 is then pumped to a filteredbrine tank 7. Next, secondary brine purification is performed on brine 3via an ion exchange unit 8. Secondary brine purification ensures highefficiency and long lasting membrane electrolyzer operation. Deionizedbrine 3 is stored in tank 9 before being sent to electrolyzer 10.

In electrolyzer 10, electric power is provided via an AC-DC rectifier11. Deionized brine 3 and purified water 12 are pumped into electrolyzer10. Application of electricity causes anions, i.e. chloride ions, tocollect at the anode side of the electrolyzer 10 and cations, i.e.potassium and hydrogen ions, to collect at the cathode side of theelectrolyzer 10. The chlorine produced from the weak solution of brine3, is either drawn from the anode side of the cell in a vacuum or thesolution is pumped to a dechlorination process.

To process the wet chlorine, the gas is cooled and the brine 3condensate is removed in a dechlorinator 14. The weak solution of brine3 is then returned to the brine treatment area, specifically the saltdissolver 2. Next, the chlorine gas is dried with a sulfuric acid dryer15. The dry gas is then compressed and chilled for storage in rail cars17. The chlorine gas may also be stored in cylinders or bulk plantstorage.

However, drying, compressing storing the chlorine gas are majordrawbacks to plant operation. Drying and compressing the chlorine isexpensive and increases the capital costs for plant operation by as muchas 10-20%. Additionally, storage of chlorine gas on-site is undesirablebecause it is potentially very hazardous and may be a terrorist target.

Potassium hydroxide and hydrogen, collected at the cathode side ofelectrolyzer 10, are drawn from the membrane cell electrolyzer 10.Potassium hydroxides leave the electrolyzer 10 at approximately 30-35%by weight in an aqueous solution at a temperature between approximately190 and 200° F. This low strength potassium hydroxide solution is split.One stream is cooled and stored for use in the brine treatment tank 5.The other, major, stream is sent to the evaporator 18 for removing thewater. In the evaporator 18, the hot potassium hydroxide solution isconcentrated to the commercial grade specification, i.e., approximately45%. Next, the product is cooled to about 170° F. and sent to productstorage 20.

Hydrogen gas, also produced on the cathode side of the electrolyzer 10,may be sent to vent 21 for pressure control. The majority of theproduced hydrogen, however, is cooled to remove water vapor before it ispumped to hydrogen compressor. After the hydrogen is compressed, it issent to the boiler 22 where it is burned as fuel.

Currently, there are many chemical plants in the United States thatproduce sodium hypochlorite by the chemically reactive combination ofchlorine and sodium hydroxide. However, current facilities require thedelivery of hazardous chlorine gas by truck or rail to the productionsite. Integration of potassium hydroxide production with bleachmanufacture is a logical combination that can both reduce transportationcosts and eliminate the need to store hazardous chlorine gas on-site.Presently, however, there are no known plants in the United States thatproduce potassium hydroxide and sodium hypochlorite by the processesaccording to the present invention.

It is anticipated that there will be a new demand for these dedicatedchlorine plants, since the Department of Homeland Security wants thepublic transportation of hazardous chlorine and chlorine storageeliminated as possible terrorist targets.

SUMMARY OF THE INVENTION

This invention described herein relates to the process for theintegrated manufacture of potassium hydroxide and bleach. Specificallythe process allows several process options that can provide economicflexibility based on the varying demands of chlorine products. Thechlorine gas that is produced via electrolysis of KCl may be solddirectly to a customer via pipeline. Alternatively, the plant operatorcan divert the chlorine production from chlorine pipeline deliveries toeither NaOCl (bleach) or HCl (hydrochloric acid) production.

The chemical reactions of the new process combination can be summarizedas follows:

2KCl+2H₂+electricity->Cl₂+2KOH+H₂

-   -   (Electrolysis of potassium chloride salt with demineralized and        deionized water yields chlorine, potassium hydroxide, and        hydrogen.)

Cl₂+2NaOH->NaOCl+H₂O+NaCl

-   -   (Chlorine reacts with purchased sodium hydroxide to yield sodium        hypochlorite, water, and sodium chloride.)

H₂+Cl₂->2HCl

-   -   (The Reaction of Hydrogen and Chlorine Produces Hydrochloric        Acid.)

The present invention is the first process of its kind to integrate theprocesses of KOH and bleach manufacture. This new process designprovides for easy economical balance and allows the plant operator toshift production based on the varying demands of the chlorine products.Further, the disclosed process eliminates the need for onsite storage ofpotentially hazardous chlorine gas.

It is therefore an object of the invention to eliminate the need for thetransportation and onsite storage of highly dangerous chlorine gas.

It is another object of the invention to provide greater productionflexibility than existing caustic potash plants.

It is still another object of the invention to offer greaterprofitability than existing caustic potash plants or electrolysis bleachplants.

It is still a further object of the invention to provide a process inwhich production of chlorine gas can be easily diverted from direct saleto production of bleach and/or hydrochloric acid.

It is yet a further object of the invention to provide a process withbetter economics than existing caustic potash plants and electrolysisbleach plants.

Other objects, features, and characteristics of the present invention,as well as the methods of operation and functions of the relatedelements of the structure, and the combination of parts and economies ofmanufacture, will become more apparent upon consideration of thefollowing detailed description with reference to the accompanyingdrawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the present invention can be obtained byreference to a preferred embodiment set forth in the illustrations ofthe accompanying drawings. Although the illustrated embodiment is merelyexemplary of systems for carrying out the present invention, both theorganization and method of operation of the invention, in general,together with further objectives and advantages thereof, may be moreeasily understood by reference to the drawings and the followingdescription. The drawings are not intended to limit the scope of thisinvention, which is set forth with particularity in the claims asappended or as subsequently amended, but merely to clarify and exemplifythe invention.

For a more complete understanding of the present invention, reference isnow made to the following drawings in which:

FIG. 1 shows a schematic of the process of producing potassium hydroxideand chlorine gas;

FIG. 2 depicts a schematic of the manufacturing process in accordancewith the preferred embodiment of the present invention;

FIG. 3 shows an expanded view of the manufacturing process in accordancewith the preferred embodiment of the present invention;

FIG. 4 is a schematic representation of a cell gas bleach reactoraccording to the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As required, a detailed illustrative embodiment of the present inventionis disclosed herein. However, techniques, systems and operatingstructures in accordance with the present invention may be embodied in awide variety of forms and modes, some of which may be quite differentfrom those in the disclosed embodiment. Consequently, the specificstructural and functional details disclosed herein are merelyrepresentative, yet in that regard, they are deemed to afford the bestembodiment for purposes of disclosure and to provide a basis for theclaims herein which define the scope of the present invention. Thefollowing presents a detailed description of the preferred embodiment(as well as some alternative embodiments) of the present invention.

This invention is applicable for a standalone plant or a plant dedicatedfor gaseous chlorine delivery to an adjacent plant for production ofhydrochloric acid, bleach, or various chemicals, which require chlorinegas as a reactant.

The present invention involves the integrated process for themanufacture of potassium hydroxide, KOH, also called caustic potash, andsodium hypochlorite. Chlorine gas that is produced by the electrolysisof a potassium chloride solution in an electrolysis cell is useddirectly in sodium hypochlorite (bleach) manufacture by chemicallycombining the chlorine with purchased sodium hydroxide. Alternatively,hydrochloric acid, HCl, may be produced by the burning of chlorine inthe presence of co-product hydrogen. Direct use of chlorine from KOHmanufacture eliminates the need for transporting or storing thehazardous chlorine gas. Further, co-product hydrogen may be collectedindependently, dried, and sold to customers.

According to the preferred embodiment of the present invention, shown inFIG. 2, solid potassium chloride (KCl) salt 41 arrives at a processingplant via rail car 44. Potassium chloride 41 is transferred to a saltdissolver 42, wherein the solid, impure potassium chloride 41 isdissolved in water to form brine 43. In an alternative embodiment,sodium chloride (NaCl) may be substituted for potassium chloride toultimately produce sodium hydroxide (NaOH) instead of potassiumhydroxide (KOH).

Next, appropriate chemicals are added to the brine 43 to precipitateimpurities that may be potentially damaging to the membrane in theelectrolyzer. Among the most common adulterants found in impure brineare sulfate ions, which may be removed by precipitation with barium orcalcium. The resulting mixture is fed to a thickener 45, from whichprecipitates and clarified raw brine 43 are separately withdrawn. Theclarified brine 43 is then filtered by brine filter 46. Solidprecipitates are sent to a landfill, or disposed of by any suitablemethod. The filtered brine 43 is then pumped to a filtered brine tank47. Next, secondary brine purification is performed on brine 43 via anion exchange unit 48. Secondary brine purification ensures highefficiency and long lasting membrane electrolyzer operation. Deionizedbrine 43 is stored in tank 49 before being sent to electrolyzer 50.

Electrolyzer 50 is preferably a single or multiple membrane electrolyzercell, as it is known to be safe, asbestos and mercury free andeffective. However, in alternative embodiments, other electrolyzers maybe used. Such commonly known electrolyzers are mercury and asbestosdiaphragm electrolyzers, and membrane electrolyzers—monopolar andbipolar.

In electrolyzer 50, electric power is provided via an AC-DC rectifier51. Deionized brine 53 and purified water 52 are pumped intoelectrolyzer 50. Application of electricity causes anions, i.e. chlorideions, to collect at the anode side of the electrolyzer 50 and cations,i.e. potassium and hydrogen ions, to collect at the cathode side of theelectrolyzer 50. The chemical equations below describe the reactionsthat take places upon electrolysis of the brine.

2Cl⁻->Cl₂+2e ⁻(Anode)

2H₂O+2e ⁻->H₂+20H⁻(Cathode)

The chlorine gas will form at the anode while the water will beelectrolyzed to form hydrogen gas. The remaining ions, K+ and OH⁻ willcombine to form an aqueous solution of the desired caustic potashproduct.

The chlorine produced from the weak solution of brine 43, is eitherdrawn from the anode side of the cell in a vacuum or the solution ispumped to a dechlorination process. To process the wet chlorine, the gasis cooled and the brine 43 condensate is removed in a dechlorinator 54.The weak solution of brine 43 is then returned to the brine treatmentarea, specifically the salt dissolver 42. According to the presentinvention, the costly steps of drying and liquefying chlorine gas areeliminated. Instead, the chlorine is pumped to the hypo tower 64.

The sodium hypochlorite, or hypo, system consists of two plate exchangescrubbing towers 64 and 66, with associated pumps, tanks, coolers andfans. Operation of the hypo system is continuous. For safety reasons,the critical equipment is provided with a secure electric power supplyto ensure continued operation during power failures and to avoidcatastrophic consequences.

In order to manufacture sodium hypochlorite, chlorine gas from thedechlorinator 54, as well as vent gases from miscellaneous sources inthe plant, are drawn by a vacuum or pumped through the primary hypotower 64. Sodium hydroxide 65 from the secondary hypo tower 66, as wellas recirculated sodium hydroxide and sodium hypochlorite from theprimary hypo tower pump, are fed to the top of the primary hypo tower64. The sodium hydroxide and chlorine react to form bleach according tothe following equation:

2NaOH+Cl₂->NaOCl+NaCl+H₂O+heat

The exothermic nature of the above reaction causes the temperature torise in the primary hypo tower 64, and therefore to maintain productstability the hypo is cooled before storage in storage tank 68. Theprimary hypo tower 64 is a plate exchanger with cooling water used tocool the liquor. The primary hypo chiller further reduces the hyposolution temperature to 60° F. using chilled water to slow down thechemical disintegration of the hypo product.

A portion of the cooled hypo product is transferred to storage tank 68by primary hypo pump through the hypo filter. The filter ensures a clearproduct solution for storage. Product in various strengths, up to 20% byweight, can be produced by controlling the balance between chlorine,sodium hydroxide, and water.

Vent gases leaving primary hypo tower 64 are piped to the secondary hypotower 66. The gas flows upward through tower 66 under suction from hypofan 67. Sodium hydroxide solution is circulated around tower 66 by thesecondary hypo tower pump and absorbs any residual chlorine from primaryhypo tower 64. Any unexpected large chlorine vents from primary hypotower 64 will be absorbed and the chlorine emissions kept to a minimumwith a two-tower scrubbing system.

The secondary hypo cooler 69 is used to remove the heat resulting fromthe reaction of chlorine in the secondary hypo tower 66, and thedilution of sodium hydroxide.

In the process that uses hypo fan 67, suction throughout the hypo systemis provided by a centrifugal fan connected to the outlet of thesecondary hypo tower 66. Effluent is scrubbed with caustic soda anddischarged to the atmosphere. The suction provided by hypo fan 67introduces an additional safety feature. In the case of a leak in thechlorine line in the hypo system, the pressure differential created byhypo fan 67 will cause air to be sucked into the line and not permitchlorine gas to escape. An installed spare fan is also provided. Bothfans are connected to the standby power supply.

An alternative embodiment for the manufacture of sodium hypochlorite isshown in FIG. 4. As discussed with respect to the preferred embodiment,the costly steps of drying and liquefying chlorine are also eliminatedin this alternative embodiment. Chlorine from electrolyzer 50, ventgases and “off spec” product are mixed with purchased sodium hydroxide80 solution to form sodium hypochlorite, i.e. hypo, solution. The system85 consists of an eductor 72, bleach reactor 74, refrigerated cooler 76,static mixer 78 and various pumps and control valves. Purchased sodiumhydroxide 80 from storage is pumped into the system.

Chlorine, saturated with water, leaves the electrolyzer 50 at atemperature of approximately 190-200° F. and is pumped through aneductor 72. Eductor 72 mixes the chlorine in solution with recycledhypo. The hypo solution enters the bleach reactor 74 where recycled,chilled hypo is pumped into reactor 74 for mixing. Then, bleach fromreactor 74 is pumped through a refrigerated cooler 76 wherespecification product is drawn off and sent to storage. Other bleach isrecycled onto the static mixer after controlled quantities of water andsodium hydroxide are added to the bleach. Through controls and analyzersfor the amount of chlorine, water, sodium hydroxide, and temperature inthe system permit the production of bleach up to 20% by weight.

Additionally, the process may be modified to manufacture hydrochloricacid, as shown in FIG. 3. The hydrogen gas generated at the cathode ofelectolyzer 50 is sent to acid burner 88. Chlorine gas that comes out ofthe dechlorinator 54 may also be sent to acid burner 88. The chlorine isthen burned in the presence of hydrogen and demineralized water providedby stream 90 to form hydrochloric acid, which is then sent to tank 92.The concentration of the acid may be controlled by the amount of waterused in the process.

Potassium hydroxide and hydrogen, collected at the cathode side ofelectrolyzer 50, are drawn from the membrane cell electrolyzer 50.Potassium hydroxides leave the electrolyzer 50 at approximately 30-35%by weight in an aqueous solution at a temperature between approximately190 and 200° F. This low strength potassium hydroxide solution is split.One stream is cooled and stored for use in the brine treatment tank 45.The other, major, stream is sent to evaporator 58 for removing thewater. In evaporator 58, the hot potassium hydroxide solution isconcentrated to the commercial grade specification, i.e., approximately45%. Next, the product is cooled to about 170° F. and sent to productstorage 60.

Hydrogen gas, also produced on the cathode side of the electrolyzer 50,may be sent to vent 61 (FIG. 3) for pressure control. The majority ofthe produced hydrogen, however, is cooled to remove water vapor beforeit is pumped to hydrogen compressor. After the hydrogen is compressed,it is sent to the boiler 62 for use as fuel. Alternatively, as discussedbefore, the collected hydrogen gas may be collected, stored and sold tocustomers, or send to acid burner 88 for use in hydrochloric acidproduction.

At a standalone plant, the present invention offers greater operatingflexibility, profitability, and safety than existing plants. Astandalone plant would produce KOH and bleach and/or HCl since thetransportation of gaseous chlorine is difficult and dangerous.Currently, there are no known plants with this processing option.

At a dedicated plant, for the situation where a customer wants to buygaseous chlorine, this combination of processes enables the economicbalancing of product production with chlorine demand. When gaseouschlorine demand is lowered, the plant operator can divert the chlorineproduction from chlorine pipeline deliveries to either bleach or HClproduction. This permits the plant to continue to operate at fullcapacity. The liquid products, KOH, bleach, and HCl are all readilystored in rail cars or storage tanks and provide the capability ofbalancing supply and demand with alternate product sales or storage.

According to the process of the present invention, bulk chlorine isnever stored under pressure in storage drums or rail cars. Thiseliminates the hazard of a chlorine cloud being releasedunintentionally. Small quantities of elemental chlorine exist only inthe process just prior to being combined with sodium hydroxide, hydrogenor in the customer pipeline. In the case of a dedicated plant, chlorineis delivered to nearby customers and eliminates the use of rail cars andonsite chlorine storage.

Further, the invention is the combination of known processes thatprovide for greater revenue and profit than existing processes. There isno existing plant that combines the electrolysis of KCl with bleach andhydrochloric acid manufacture and has pipeline delivery of chlorine.

In addition, the hydrochloric acid and bleach manufacture of the presentinvention adds flexibility to consume the chlorine production when otherchlorine derivative requirements are low.

According to another aspect of the present invention, the process,compared to existing potassium hydroxide-chlorine plants, eliminates theneed for expensive chlorine drying and liquefaction. Two hypo towers,bulk sodium hydroxide storage, pumps, and lines are added to theprocess. It is estimated that the net capital cost is reducedsignificantly with the invented process.

While the present invention has been described with reference to one ormore preferred embodiments, such embodiments are merely exemplary andare not intended to be limiting or represent an exhaustive enumerationof all aspects of the invention. The scope of the invention, therefore,shall be defined solely by the following claims. Further, it will beapparent to those of skill in the art that numerous changes may be madein such details without departing from the spirit and principles of theinvention. It should be appreciated that the present invention iscapable of being embodied in other forms without departing from itsessential characteristics.

1. A method of manufacturing a sodium bleach and an alkali metalhydroxide solution comprising potassium hydroxide, said methodcomprising the steps of: providing an aqueous solution of a chloridesalt comprising potassium chloride; precipitating out impurities fromsaid aqueous solution of said chloride salt by adding at least one of abarium or calcium chemical to form a precipitated aqueous solution;secondary purification of said precipitated aqueous solution bypurifying said precipitated aqueous solution through an ion exchangeunit to form a secondary precipitated aqueous solution; electrolyzingsaid secondary precipitated aqueous solution to collect chlorine gas atan anode and to collect hydrogen gas at a cathode, and to form anaqueous alkali metal hydroxide solution; pumping the chlorine gas to adechlorinator and cooling said chlorine gas to form cooled chlorine gas;removing brine condensate from said cooled chlorine gas to form driedchlorine gas; pumping said dried chlorine gas to a hypo system to bemixed with stored sodium hydroxide, wherein said hypo system comprises aplate exchanger with cooling water; and combining said dried chlorinegas with said stored sodium hydroxide to form a sodium bleach.